The present inventor is the applicant in several previous United States patent applications, in particular U.S. application Ser. No. 07/608,850 filed Nov. 5, 1990 and issued as U.S. Pat. No. 5,188,692; and its Divisional application Ser. No. 07/779,263, filed Oct. 18, 1991 and issued as U.S. Pat. No. 5,250,146.
The previous patent applications teach an apparatus and method for laminating a layer of non-oriented polymer plastic to a precast layer of glass for much the same purposes as described above, and the present invention is particularly directed to improvements beyond the apparatus and methods as previously taught.
The automotive glass industry is, so far, highly labour intensive. For example, the preparation of a windshield or side window for an automobile very often requires a hand lay-up of the non-oriented plastic film to the glass. After the plastic film has been placed on the glass and perhaps most of the air bubbles caught between the film and the glass removed by use of a squeegee, a vacuum ring or other device may be placed around the periphery to pull as much air as possible from between the film and the glass. Thereafter, the glass/plastic film combination may be placed into an autoclave which is then pressurized and heated so as to adhere the non-oriented plastic film to the glass under the pressure and heat conditions.
Most often, in such a structure the plastic film may be a composite laminar structure of non-oriented polyvinyl butyryl together with oriented polyethylene teraphthalate (PVB/PET), or it may be a composite laminar film of non-oriented polyurethane together with polyethylene teraphthalate; or it may be PVB or polyurethane. The polyvinyl butyryl (or polyurethane) is a generally soft non-oriented material which is quite often slightly embossed and somewhat opaque because of its surface character. However, the apparent opacity of the PVB disappears when the film surface is smooth, or is made smooth under the action of heat and/or pressure. The polyethylene teraphthalate is an oriented tough film which provides anti-lacerative characteristics to the glass/plastic film structure, because glass will shatter upon impact. The PVB layer adheres the PET layer to the glass, and also provides energy absorption in the event of impact with the composite laminar structure. Thus, the PET layer provides a barrier to protect a person from shattered glass shards in the event of an accident.
It is a characteristic of polymer plastic films as discussed herein that if there are any significantly large air bubbles entrapped in the interface between that film and glass, the bubbles may remain after heat and pressure treatment, particularly as in the prior art. However, if very small air bubbles are entrapped, and particularly if the film layer is PVB, they will be absorbed by the PVB. The difficulty is that significant air bubbles at the interface between the PVB and glass, or at the PVB/PET interface, or wrinkles that may occur in the PVB or PET, will materially affect the optics of the glass/plastic film laminar structure in that an object viewed through the glass/plastic film laminate structure may appear to be distorted. This may be especially important in the event of use of glass/plastic film laminar structures as side windows of automobiles or other vehicles, since such windows are generally unframed, and the incidence of air bubbles or wrinkles especially near the edges of the glass is not acceptable.
As it happens, in a simple laminated structure having glass together with PVB/PET, the composite layer of non-oriented PVB polymer plastic film together with oriented PET polymer plastic film is applied to the inside surface of the glass--that is, to the concave side of the curve if the precast glass is curved, which will be the inside surface of the windshield or side window when in use.
The autoclave procedure to adhere a non-oriented plastic film to glass required several hours per cycle, and it is not possible until the after the cycle has finished to determine if the glass/plastic film laminate workpiece being produced is acceptable. In other words, there is no determination of scrap (other than breakage) until after the autoclave cycle has been concluded. Moreover, the amount of unusable workpieces which become scrap may be high, so that the prior art autoclave production methods may be significantly inefficient as to the use of labour, the use of time, and particularly as to the use of energy.
In the meantime, the use of glass to which a polymer plastic film has been adhered as a windshield or as a side window of automobiles and the like has been approved, and it is expected that such use may become mandatory. In particular, use of such laminated glass/plastic film structures as side windows is a significant safety step as there is little that can be done to preclude impact of an object against the side window in the event of an accident where there may be relative sideways movement of any object to the side window; whereas the increasing use of seat belts--the use of which is mandatory in most jurisdictions--and the increasing use of air bags may reduce the chance of impact, particularly of the head of a driver or passenger against the windshield of an automobile.
The production of PVB/PET having uniform thickness is highly desirable, but is difficult if not nearly impossible to achieve using any known prior art laminating apparatus method. Non-uniform thickness of PVB/PET may result in distortion which is visible. Lack of uniform thickness may be present in some or all of three ways, as described below.
One way is characterized by the thickness of the plastic film layer changing over the surface of the precast layer of glass so as to conform to minor irregularities in the surface of the glass. In contrast, the opposite side of the plastic film conforms to the different irregular shape as caused by the surface of the contact surface of the ram. Resultingly, the thickness of the plastic film after it has been applied to the glass tends to vary enough across the surface of the windshield so as to cause unacceptable visual distortion. This above described problem can be overcome through the use of a ram having a contact portion that is specifically contoured to conform to the shape of the upper surface of the precast layer of glass.
A second way is characterized by the thickness of the plastic film increasing or decreasing, as the case may be, from one edge of the precast layer of glass toward an opposite edge. This overall change in thickness is caused by the lower surface of the ram being oriented at a slight angle to the upper surface of the glass. The plastic film is in essence squeezed to conform to this slightly angled shaped. This above described problem can be overcome through the use of a ram that adapts to any angular discrepancy between the ram and the precast layer of glass.
A third way is characterized by the thickness of the plastic film over the surface of the precast layer of glass as the plastic film is stretched over the precast layer of glass during its application. The stretching of the plastic film causes a corresponding decrease in the thickness of the film. For the film to be of a constant thickness, the decrease as caused by the stretching must also be constant. Accordingly, the plastic film must be stretched evenly during its application. This can be accomplished by clamping the plastic film at a pre-calculated shape and size near its perimeter in such a manner so as to preclude slippage of the plastic film. Clamping of the film so as to preclude slippage is very difficult, especially with PET. This above described problem can be overcome through the use of a toothed-clamping means that punctures the plastic film. Further, the pre-calculated shape and size of the clamping means must permit even stretching of the pre-cast layer of polymer plastic film retained therewithin.
The present inventor has noted that the relatively soft PVB (or polyurethane) non-oriented plastic film layer may indeed act as a gauge when a ram or pusher is being used to press the film against the glass. What this does is to permit a slight adjustment of the glass and the pusher ram acting against it, and this phenomenon occurs as a function of the temperature and/or pressure working on the PVB. In any event, because cold or warm PVB has a moderate tensile strength, it is possible to push a ram against the film and to contact it against the glass--the details of which are discussed hereafter--so that when the film and glass are fully contacted in a manner that substantially precludes any large air bubbles to have occurred, the structure may be heated to the laminating temperature of the PVB.